a homeostatic drive to sleep that increases during wake and decreases during sleep. Today, the two process model is used as the basis for most predictive models of sleep and performance. Annual timing of reproduction Apart from daily alternations in the environment, there are substantial seasonal variations that animals must adapt to across the year. Working with Drent, Daan showed that one strategy used to deal with seasonal changes is to adjust the number and even sex of offspring. Organisation Serge Daan held many offices in academia. He was member of the board of Earth and Life Sciences of NWO – the Netherlands Organisation for Scientific Research (1997–2002), and chairman of the NWO program Evolution and Behaviour (2002–2009). He was president of the Dutch Society for Behavioural Biology (1996–2001). From 2001 to 2004 he was vice-dean for research at the Faculty of Mathematics and Natural Sciences of the University of Groningen, and together with dean D.A. Wiersma was responsible for incisive changes such as the tenure track system and the Rosalind Franklin fellowships for women. From 2007 till 2009 he was dean of this Faculty. Teaching Serge Daan taught a wide array of courses on all levels of the curriculum of Biology (animal ecology, zoology, human ethology, chronobiology, animal behaviour, evolution), including the recent tutorial Honours College for highly talented students. He supervised more than 200 master students during their research projects. Serge Daan took the initiative to set up and coordinate the top-master program in Behavioural and Cognitive Neurosciences at the University of Groningen, the Netherlands. Ph.D.s supervised To date, Daan has supervised 43 Ph.D. students. 1986 D. Masman: The annual cycle of the kestrel, Falco tinnunculus. A study in behavioural energetics. 1988 C. Dijkstra: Reproductive tactics in the Kestrel, Falco tinnunculus. A study in evolutionary biology. 1988 T. Meijer: Reproductive decisions in the Kestrel, Falco tinnunculus. A study in physiological ecology. 1988 D.J. Dijk: Spectral analysis of the sleep EEG. Experiments inspired by the two-process model of sleep regulation. (cum laude) 1989 J.H. Meijer: Neuropharmacological and photic manipulation of the circadian pacemaker. 1991 M.P. Gerkema: Ultradian and circadian oscillators in the temporal organization of behaviour in voles. 1993 P.C.J. Franken: Sleep homeostasis and brain temperature. Experimental and simulation studies in the rat. 1995 S. Verhulst: Reproductive decisions in the Great Tit: An optimality approach. (cum laude) 1995 M.W.G. Brinkhof: Timing of reproduction. An experimental study in coots. 1996